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Activation of Phospholipase C Increases Intramembrane Electric Fields in N1E-115 Neuroblastoma Cells

Department of Physiology and Center for Biomedical Imaging Technology, University of Connecticut Health Center, Farmington, Connecticut 06030

Correspondence: Address reprint requests to Leslie M. Loew, Dept. of Physiology and Center for Biomedical Imaging Technology, University of Connecticut Health Center, Farmington, CT 06030. E-mail: les{at}volt.uchc.edu.

We imaged the intramembrane potential (a combination of transmembrane, surface, and dipole potential) on N1E-115 neuroblastoma cells with a voltage-sensitive dye. After activation of the B₂ bradykinin receptor, the electric field sensed by the dye increased by an amount equivalent to a depolarization of 83 mV. The increase in intramembrane potential was blocked by the phospholipase C (PLC) inhibitors U-73122 and neomycin, and was invariably accompanied by a transient rise of [Ca²⁺]_i. A depolarized inner surface potential, as the membrane loses negative charges via phosphatidylinositol 4,5-bisphosphate (PIP₂) hydrolysis, and an increase in the dipole potential, as PIP₂ is hydrolyzed to 1,2-diacylglycerol (DAG), can each account for a small portion of the change in intramembrane potential. The primary contribution to the measured change in intramembrane potential may arise from an increased dipole potential, as DAG molecules are generated from hydrolysis of other phospholipids. We found bradykinin produced an inhibition of a M-type voltage-dependent K⁺ current (I_K(M)). This inhibition was also blocked by the PLC inhibitors and had similar kinetics as the bradykinin-induced modulation of intramembrane potential. Our results suggest that the change in the local intramembrane potential induced by bradykinin may play a role in mediating the I_K(M) inhibition.

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